The present invention relates generally to gaseous absorption spectroscopy, to passive radiometric thermometry, to hygrometers, and more particularly to measurement of gaseous component vapor densities and saturation ratios in multicomponent, multiphase systems which may contain aerosols and may be supersaturated in the sampled component or other gases.
Measurement of gaseous component vapor density by means of radiation absorption at wavelengths selective to the sensed molecule is commonplace and has been practiced since the turn of the century. For example, U.S. Pat. No. 4,157,470 describes such a system and is typical of the art. Similarly, passive radiative gas thermometry by means of broadband Plankian emission is commonplace as typified by U.S. Pat. No. 4,120,200. Measurement of gaseous component vapor density at saturation ratios less that 1.00 is routinely accomplished by a variety of gravimetric, spectroscopic, chemical, condensation point, hygroscopic equilibrium, psychrometric, vapor adsorbtion, gaseous conductivity and other techniques.
Measurement of gas component vapor density and saturation ratio in supersaturated conditions where the saturation ratio can be in excess of 1.00 has not been routinely accomplished due to the extreme thermodynamic instability of such conditions. Recently Gerber in U.S. Pat. No. 4,083,249 has proposed a supersaturation hygrometer that operates by means of monodisperse submicron salt particles on a hydrophobic substrate in feedback equilibrium with an infrared heater. His device operates only in a very narrow supersaturation range, at temperatures warmer than the freezing point of water, and in the relative absence of hydrometeors. A literature search has disclosed no existing device which is capable of measuring arbitrary supersaturations with respect to either solid or liquid phases of the sensed molecule in multi-phase, multi-component systems which may contain dispersed aerosols or be at temperatures lower than the freezing point of the sensed molecule. Yet such supersaturations are very important to a variety of industries and scientific disciplines. To cite only a single example from the field of meteorology; atmospheric water supersaturations with respect to ice or liquid water are the dominant mid and high latitude precipitation forming mechanism, mediate most weather modification efforts, influence aircraft icing, dominate contrail formation and provide a means where heavy commercial airline traffic influences the earth's local climate and thermal radiation budget. A device capable of making such measurements would thus be of relevance to the field of meteorology.